[FEATURE] Force players on mounts

[diademiemi]

A start line should be able to force players on mounts, such as a boat, pig or horse.
The syntax for this could be
ln line a_start_line mount boat
It should be possible to specify NBT too to give horses a certain speed and boats a wood type.
This will spawn a boat for every player and have them enter it.
The plugin should also cancel exits with ln line a_start_line mount allowexit false which will be the default.
This will prevent players from exiting the boat until the line has finished, it should still allow them to exit by teleporting out.
Teleports done by the plugin itself (Such as from illegal areas) should keep the players in boats.

The feature can be disabled with ln line a_start_line mount disabled
I don't expect this to work well with high player counts, since if a lot of players are waiting and they all get put in boats or other entities (With a larger hitbox) this could create a lot of entity cramming, but if players are given enough space this should be fine.